PROJECT SUMMARY/ABSTRACT Natural fertility requires spermatozoa to migrate through viscoelastic secretions and to overcome the physiolog- ical acidic environment of the female reproductive tract. Our preliminary data show that novel mucoadhesive, bioresponsive polymer compositions maintain a physiologically acidic pH environment upon exposure to seminal fluid and, at the same time, dramatically increase viscoelastic properties, which negatively impacts sperm motil- ity. Therefore, it is hypothesized that - upon exposure to semen - the novel mucoadhesive, bioresponsive com- position rapidly transforms the vaginal cavity into an inhospitable environment for sperm. We propose to explore an innovative approach to on-demand non-steroidal contraception for women using SMART (= System Mute until Activation by a Remote Trigger) polymer fibers that maintain a physiological, protective vag- inal environment upon exposure to seminal fluid resulting in infertility. This high-risk/high-reward research strategy is fundamentally different from conventional nonsteroidal contraceptive methods as it represents an innovative bioengineering concept intended to reach the human testing phase (i.e., IND milestone) much faster and at a lower cost than conventional development programs focusing on medicinal chemistry approaches. In the R61 Phase, we will test whether non-woven fiber mats comprised of bioresponsive polymer mixtures establish an acidic mucoadhesive gel phase upon exposure to vaginal fluid that maintains a physiologically pro- tective highly viscous, acidic milieu in the presence of semen, thereby inhibiting sperm motility to a level con- sistent with infertility. The feasibility of this approach has been shown using polymeric fiber mats produced by electrospinning that demonstrated rapid conversion into a gel phase, which maintained acidic properties upon exposure to alkaline seminal fluid while, simultaneously, increasing 5-fold in viscosity. In Aim #1, we will delineate electrospinning fabrication parameters required to prepare dry, non-woven fiber mats that exhibit desired muco- adhesive and bioresponsive properties. We will test their ability to rapidly reconstitute into an acidic gel phase and maintain effective physical and chemical barriers properties for human sperm that are consistent with infer- tility. In Aim #2, we will define safety risks of non-woven polymeric fiber mats for nonsteroidal contraception. We will assess whether polymeric fiber mats are toxic to cells of the female reproductive tract. In addition, we will explore human factors that contribute to use-related safety and efficacy risks using internet surveys. The R33 Phase will be initiated only if quantitative milestones defined for the R61 Phase are met. In Aim #3, we will refine electrospinning fabrication process and perform a more rigorous in vitro safety assessment that includes inter- actions with the vaginal microbiome. In the final Aim #4, we will determine the safety, tolerability, and contracep- tive efficacy of the most promising polymer composition in vivo using the rabbit animal model.